Hydrocarbons are obtained from subterranean formations by drilling through a well that penetrates the formation. This provides a partial flow-path for the hydrocarbons to reach the surface. In order for the hydrocarbons to be produced, there must be a sufficiently unimpeded flowpath from the formation to the wellbore to be pumped to the surface. Some wells need to be stimulated due to insufficient porosity or permeability of the formation. Common stimulation techniques include hydraulic fracturing and acidizing operations. The efficiency in hydrocarbon recovery from such stimulation techniques is dependent on the development of sufficient channels for the flow of hydrocarbons from low permeability regions of the formation.
During hydraulic fracturing, a fracturing fluid, typically a gelled or thickened aqueous solution containing proppant is injected into the wellbore under high pressure and injection rates. Once natural reservoir pressures are exceeded, the fluid induces a fracture in the formation and transports the proppant into the fracture. The fracture generally continues to grow during pumping and the proppant remains in the fracture in the form of a permeable pack that serves to “prop” the fracture open. The fractures radiate outwardly from the wellbore and extend the surface area from which oil or gas drains into the well. The proppant pack forms a highly conductive pathway for hydrocarbons and/or other formation fluids to flow into the wellbore.
An efficient fracturing fluid should possess good proppant transport characteristics. Such characteristics are dependent on the viscosity of the fluid. Generally, the viscosity should be high in order to achieve wider and larger fractures. High viscosity is further generally desirable for more efficient transport of proppant into the fractured formation. The fracturing fluid therefore typically contains a viscosifying agent, such as a viscoelastic surfactant or a polymer. The polymer may be linear or crosslinked. In certain formations, aqueous acid solutions can be used to improve the permeability of the formation, thereby increasing hydrocarbon production. These acids are often combined with polymeric gels to provide an acid fracturing fluid.
A wide range of additives may be used to enhance the rheological properties and/or the chemical properties of the fluid. Such additives include viscosifiers, friction reducing agents, surface active agents and fluid loss control additives.
After the fracturing fluid is injected into the formation and fractures have been established, production of hydrocarbons is enhanced through the new fractures by removal of the viscous fluid. Generally, the viscosity of the fluid may be decreased by introducing breakers into the formation which degrade the polymer or break the emulsion. However, breakers often result in incomplete breaking of the fluid and/or premature breaking of the fluid before the fracturing process is complete.
Similar to stimulation fluids, other fluids used to treat wells must be removed following the completion of the treatment operation for which such fluids are used. For instance, polymeric viscosifying agents frequently used in drilling muds and well completion fluids have a damaging effect since they tend to interfere with other phases of drilling and/or completion operations, as well as production of the well after such operations are finished. For example, drilling fluids tend to seep into the surrounding formation forming a filter cake on the wall of the wellbore. The filter cake sometimes can prevent casing cement from properly bonding to the wall of the wellbore. It is important in such operations that the viscosifying agents and other components of the drilling mud be removed from the well in order to enhance the recovery of hydrocarbons. Oxidative breakers and enzymes are often used to degrade the polysaccharide-containing filter cakes and residual damaging materials which reduce their viscosity.
As an alternative to the use of breakers, or for use in conjunction with breakers, flowback additives are often introduced into the well to assist in the removal of well treatment fluids. Flowback additives are typically surfactants. Such surfactants reduce the surface tension between the treatment fluid and hydrocarbons. For instance, in the recovery of hydrocarbon gases, flowback additives enable the recovery of more fluid which restores the formation's relative permeability to gas. In addition to fracturing and acidizing operations, there is a need for such flowback additives for use in other treatment operations, such as sand control operations.
While conventional surfactants have been widely used as flowback additives for the removal of treatment fluids from the formation and well, such surfactants are not environmentally friendly. The need exists for alternative flowback additives which are biodegradable, non-toxic, and biocompatible and which are based on renewable resources.